1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device which has color filter layers on a substrate on which active elements are formed.
2. Description of the Related Art
As a liquid crystal display device which is capable of performing color display of high definition served for a notebook type computer, a computer monitor or a television receiver set, an active matrix type liquid crystal display device has been popularly used. This type of liquid crystal display device includes a so-called liquid crystal panel which substantially sandwiches a liquid crystal layer between two sheets of substrates at least one of which is formed of a transparent substrate such as a glass plate or the like. On a periphery of the liquid crystal panel, drive circuits (drive ICs) and wiring and the like are mounted or formed. Further, the liquid crystal panel is combined with a control circuit board and, when necessary, an auxiliary illumination device such as a backlight to form a liquid crystal display device. Hereinafter, even when the explanation relates to the constitution of the liquid crystal panel per se, the explanation is made as that of the liquid crystal display device for convenience's sake.
There has been known a so-called vertical electric field type (TN type) liquid crystal display device, wherein active elements such as thin film transistors, thin film diodes or the like and pixel electrodes driven by the active elements are formed on one substrate (referred to as “first substrate” hereinafter) of the liquid crystal display device and common electrodes which form an electric field for driving liquid crystal between the common electrodes and the pixel electrodes are formed on another substrate (referred to as “second substrate” hereinafter) of the liquid crystal display device. As the literature which discloses this type of active matrix type liquid crystal display device, JP-A-63-309921 can be named, for example.
On the other hand, a so-called lateral electric field type (IPS type) liquid crystal display device which forms the above-mentioned common electrodes on the first substrate side and sets the direction of an electric field applied to a liquid crystal layer arranged substantially parallel to a surface of the substrate has been put into practice. As literatures which disclose this IPS type liquid crystal display device, JP-B-63-21907 and the like which aim at the acquisition of an extremely wide viewing angle using comb-teeth electrodes at one of two substrate can be named.
In the above-mentioned respective types of liquid crystal display devices, color filter layers in three colors are provided to the first substrate or the second substrate for performing the full color display. Although a type of structure which forms these color filter layers at the second substrate side has been well known, there also exists a type of structure which forms the color filter layers on the first substrate side. In both types, the color display is obtained by performing the color modulation of light which passes the liquid crystal layer sandwiched between the pixel electrodes selected by the active elements and the common electrodes by the color filter layers.
In general, the first substrate is also referred to as “the active matrix substrate” since the active matrix elements such as thin film transistors for driving pixels are arranged thereon in a matrix array. Hereinafter, the explanation is made by calling the first substrate as the active matrix substrate and the active elements as thin film transistors. The method which forms the color filter layers on the active matrix substrate has an advantage that a step for overlapping the active matrix substrate and the second substrate which are arranged to face each other in an opposed manner is facilitated. Hereinafter, the second substrate is referred to as the counter substrate.